The production of mineral fibers such as glass fibers by a rotary process is well known. In this process, molten glass is fed at a high temperature into a metallic spinner which revolves at a high rotation rate. The spinner has a peripheral wall containing a multiplicity of orifices. The molten glass flows by centrifugal force through the orifices and forms small diameter molten glass streams. The streams are directed downward toward a collection surface by an annular blower which surrounds the spinner. The flow generated by the blower attenuates the molten glass streams into a finer diameter, and the streams are cooled to form glass fibers. An annular burner is also positioned around the spinner, and combustion gases and heat from the burner are directed downward to provide a fiber attenuating environment suitable for allowing the initial streams of glass to be attenuated to the desired final diameter. The downward annular flow of hot gases facilitates attenuation of the streams of molten mineral material into mineral fibers by the blower, and also maintains the spinner at a temperature suitable for fiberizing.